1. Field of the Invention
The present invention relates to a camera module, and in particular to a camera module, for example, a CMOS camera module, including a holder for holding a solid-state imaging device and a lens.
2. Description of the Related Art
A CMOS camera module, including a lens holder for holding a solid-state imaging device such as a CCD or the like and a lens unit having a lens for guiding light to the solid-state imaging device, is widely used for, for example, a cellular phone or a mobile terminal.
FIG. 10 shows a manner of assembling a conventional CMOS camera module 90. The CMOS camera module 90 includes a sensor 1 as a solid-state imaging device such as a CCD or the like, a lens unit 2 having a lens 8 for guiding light to the sensor 1, and a lens holder 93 for holding the sensor 1 and the lens unit 2. The lens holder 93 includes a holder base 94 having a general shape of rectangular parallelepiped and a generally cylindrical, hollow lens coupling section 95 provided on a central portion of a top surface of the holder base 94. The sensor 1 also has a general shape of rectangular parallelepiped and is smaller than the holder base 94. The sensor 1 is accommodated in the holder base 94. The sensor 1 includes a semiconductor chip, which is protected by a glass lid. The glass lid encapsulates the semiconductor chip. Even if dust adheres to the glass lid, the dust can be wiped off.
The lens unit 2 is generally cylindrical and has an outer diameter which is substantially the same as an outer diameter of the lens coupling section 95. The lens unit 2 can be coupled with the lens coupling section 95 through threads as follows. In a portion of an outer circumferential surface of the lens unit 2 close to the lens holder 93, a male thread 10 is formed. In an inner circumferential surface of the lens coupling section 95, a female thread 9 is formed which is engageable with the male thread 10.
When the lens unit 2 is inserted into the lens coupling section 95 while rotating the lens unit 2 in a prescribed direction, the male thread 10 of the lens unit 2 and the female thread 9 of the lens coupling section 95 are engaged with each other. When the lens unit 2 is further rotated in the same direction, the lens unit 2 becomes closer to the sensor 1 in a direction of an optical axis of the lens unit 2. When the lens unit 2 is rotated in the opposite direction, the lens unit 2 becomes farther from the sensor 1 in the direction of the optical axis of the lens unit 2. In this manner, the lens 8 in the lens unit 2 is focused on the sensor 1 by adjusting the distance between the lens unit 2 and the sensor 1 in this manner while checking an image obtained by the sensor 1 using an imaging jig (not shown). (The operation of focusing the lens unit 2 on the sensor 1 will be referred to as “focus adjustment”.) When the lens 8 in the lens unit 2 is focused on the sensor 1, an adhesive is caused to flow into a space between the female thread 9 and the male thread 10 so as to secure the lens unit 2 to the lens coupling section 95.
In order to strongly secure the lens unit 2 to the lens coupling section 95 of the lens holder 93, the entirety of the space between the female thread 9 and the male thread 10 needs to be filled with the adhesive. However, it is difficult to fill the space entirely. Even if this is possible, the amount of the adhesive provided in the space is insufficient to strongly secure the lens unit 2 to the lens coupling section 95 due to the narrowness of the space.
A camera module incorporated into a product, such as a cellular phone, is possibly exposed to an external force such as an impact. Unless the lens unit 2 and the lens holder 93, both included in the camera module, are secured strongly to each other, the distance between the sensor 1 and the lens unit 2 is changed from a prescribed distance. This may undesirably defocus the lens 8 in the lens unit 2 from the sensor 1, which results in the image obtained by the sensor 1 being blurred.
In the camera module incorporated into a cellular phone or the like, when the lens unit 2 and the lens holder 93 are exposed outside so as to be touched by a user or the like, electrostatic charges generated by a human hand is transferred to the lens holder 93. The glass lid for encapsulating the semiconductor chip, which is provided in the sensor 1, usually cannot shield electrostatic charges. Therefore, when the electrostatic charges are transferred to the semiconductor chip accommodated in the lens holder 93, the semiconductor chip may malfunction or be destroyed.